> Is there a more elegant solution that I've missed?

there are solutions short of using three stylesheets but none are very
nice. 
eg replace

match="h1" by
match="*[name(.)='h1' and (starts-with(namespace(.),$html-common-part))]"

in all patterns of the stylesheet.

> Does the spec need revision to accomodate this?  Or are we just stuck?

XHTML isn't a REC yet. There is still time to complain.

David


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